U.S. patent application number 13/590764 was filed with the patent office on 2013-03-14 for heat recovery system of the boiler with co2 capture system.
This patent application is currently assigned to Hitachi, Ltd.. The applicant listed for this patent is Masato Kaneeda, Shuichi Kanno, Hisayuki Orita, Hiroki Sato, Kohei Yoshikawa. Invention is credited to Masato Kaneeda, Shuichi Kanno, Hisayuki Orita, Hiroki Sato, Kohei Yoshikawa.
Application Number | 20130062883 13/590764 |
Document ID | / |
Family ID | 46754904 |
Filed Date | 2013-03-14 |
United States Patent
Application |
20130062883 |
Kind Code |
A1 |
Kaneeda; Masato ; et
al. |
March 14, 2013 |
Heat Recovery System of the Boiler with CO2 Capture System
Abstract
A boiler system including an electric power generation system
having a boiler, a steam turbine for generating electric power by
steams which received heat at a boiler, a condenser provided at the
downstream thereof for condensing the steams, and a heater for
heating condensed water by steams extracted from the steam turbine
and, further, a CO.sub.2 capture system of sorbing and capturing a
CO.sub.2 gas in an exhausted gas exhausted from the boiler by using
a solid CO.sub.2 sorbent, and a chimney of exhausting an exhaust
gas in the CO.sub.2 capture system after recovery of CO.sub.2 or an
exhaust gas exhausted from the boiler, in which the temperature of
a fluid concerned with the boiler system is increased by using the
exhaust gas exhausted from the CO.sub.2 capture system.
Inventors: |
Kaneeda; Masato;
(Hitachinaka, JP) ; Sato; Hiroki; (Hitachinaka,
JP) ; Yoshikawa; Kohei; (Hitachi, JP) ; Kanno;
Shuichi; (Hitachinaka, JP) ; Orita; Hisayuki;
(Hitachinaka, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kaneeda; Masato
Sato; Hiroki
Yoshikawa; Kohei
Kanno; Shuichi
Orita; Hisayuki |
Hitachinaka
Hitachinaka
Hitachi
Hitachinaka
Hitachinaka |
|
JP
JP
JP
JP
JP |
|
|
Assignee: |
Hitachi, Ltd.
Tokyo
JP
|
Family ID: |
46754904 |
Appl. No.: |
13/590764 |
Filed: |
August 21, 2012 |
Current U.S.
Class: |
290/52 ; 110/203;
60/681; 60/691; 60/692 |
Current CPC
Class: |
Y02C 10/04 20130101;
Y02E 20/326 20130101; Y02C 10/08 20130101; Y02C 10/06 20130101;
Y02E 20/32 20130101; Y02E 20/18 20130101; Y02C 20/40 20200801; F22B
1/18 20130101; Y02E 20/16 20130101 |
Class at
Publication: |
290/52 ; 60/692;
60/691; 60/681; 110/203 |
International
Class: |
F01D 15/10 20060101
F01D015/10; F23J 15/00 20060101 F23J015/00; F01K 19/00 20060101
F01K019/00; F01K 9/02 20060101 F01K009/02; F22D 1/00 20060101
F22D001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 12, 2011 |
JP |
2011-197834 |
Claims
1. A boiler system comprising: an electric power generation system
including: a boiler; a steam turbine which generates electric power
by steams which received heat at a boiler; a condenser produced at
the downstream thereof for condensing the steams; and a heater
which heats condensed water by steams extracted from the steam
turbine; and further a CO.sub.2 capture system which sorbs and
captures a CO.sub.2 gas in an exhausted gas exhausted from the
boiler by using a solid CO.sub.2 sorbent; and a chimney which
exhausts an exhaust gas after recovery of CO.sub.2 in the CO.sub.2
capture system or an exhaust gas exhausted from the boiler, wherein
the system has a device of increasing the temperature of the fluid
concerned with the boiler system by using the exhaust gas exhausted
from the CO.sub.2 capture system.
2. The boiler system according to claim 1, wherein the fluid is
water condensed by the condenser.
3. The boiler system according to claim 1, wherein the fluid is a
gas flowing into the boiler.
4. The boiler system according to claim 1, wherein the fluid is an
exhaust gas flowing into the chimney.
5. The boiler system according to claim 2, wherein the device of
increasing the temperature of the fluid concerned with the boiler
system by using the exhaust gas exhausted from the CO.sub.2 capture
system is a heat exchanger of increasing the temperature of water
condensed by the condenser partially or entirely by using the
exhaust gas exhausted from the CO.sub.2 capture system.
6. The boiler system according to claim 3, wherein a heat exchanger
is provided for the exhaust gas exhausted from the boiler, and the
temperature of a portion or the entirety of water condensed by the
condenser is increased by using the heat exchanger and the
temperature of the gas flowing into the boiler is increased by
using the exhaust gas exhausted from the CO.sub.2 capture
system.
7. The boiler system according to claim 6, wherein the device of
increasing the temperature of the gas flowing into the boiler by
using the exhaust gas exhausted from the CO.sub.2 capture system is
a device of using the exhaust gas exhausted from the CO.sub.2
capture system partially or entirely as the gas flowing into the
boiler.
8. The boiler system according to claim 6, wherein a heat exchanger
is provided as a device for increasing the temperature of the gas
flowing into the boiler by using the exhaust gas exhausted from the
CO.sub.2 capture system, and the heat exchanger increases the
temperature of the gas by heat exchange with the exhaust gas
exhausted from the CO.sub.2 capture system.
9. The boiler system according to claim 4, wherein the system for
increasing the temperature of the fluid concerned with the boiler
system by using the exhaust gas exhausted from the CO.sub.2 capture
system has a device of increasing the temperature of the gas
flowing into the chimney by using the exhaust gas exhausted from
the CO.sub.2 capture device.
10. The boiler system according to claim 9, wherein the device for
increasing the temperature of the gas flowing into the chimney by
using the gas exhausted from the CO.sub.2 capture system is a
system in which the gas flowing into the chimney contains exhaust
the gas exhausted from the CO.sub.2 capture system.
11. The boiler system according to claim 9, wherein a heat
exchanger is provided to the upstream of the chimney as a device
for increasing the temperature of the gas flowing into the chimney
by using the exhaust gas exhausted from the CO.sub.2 capture
system, and the heat exchanger increases the temperature of air
flowing into the chimney by heat exchange with the exhaust gas
exhausted from the CO.sub.2 capture system.
12. The boiler system according to claim 1, wherein the gas
introduced into the CO.sub.2 sorption column of the CO.sub.2
capture system is at least one member selected from a boiler
exhaust gas, CO.sub.2 gas, steams, and air.
13. The boiler system according to claim 1, wherein CO.sub.2
sorption columns are provided in plurality as the CO.sub.2 capture
system, in which a gas flowing out of the CO.sub.2 sorption column
is caused to flow into other CO.sub.2 sorption column.
14. The boiler system according to claim 1, wherein a solid
CO.sub.2 sorbent used for the CO.sub.2 capture system contains Ce.
Description
PRIORITY STATEMENT
[0001] The present application hereby claims priority under 35
U.S.C. .sctn.119 on Japanese patent application number JP
2011-197834 filed Sep. 12, 2011, the entire contents of which is
hereby incorporated herein by reference.
BACKGROUND
[0002] The present invention concerns a heat recovery system of a
boiler with a CO.sub.2 capture system.
[0003] In recent years, reduction of CO.sub.2 emission has been
demanded world wide for suppressing global worming. Particularly,
exhaust gases discharged from equipment such as coal-fired boilers,
gas turbines, and chemical plants contain CO.sub.2 as much as
several % or more and a method of separating and capturing CO.sub.2
has been demanded.
[0004] An exhaust gas processing system of a coal-fired boiler
includes an NO.sub.x reduction system provided downstream of a
boiler for reduction and detoxification of nitrogen oxides
(hereinafter referred to as NO.sub.x), an air heater provided
downstream thereof for cooling an exhaust gas using air as a
coolant, a heat exchanger provided downstream thereof for cooling
the exhaust gas using water as a coolant, a dust removal system
provided downstream thereof for removing dusts and soots in the
exhaust gas, a desulfurization system provided downstream thereof
for absorption and detoxification of sulfur oxide (hereinafter
referred to as SO.sub.x), and a heat exchanger provided downstream
thereof for warming the exhaust gas (for example, refer to IHI
Technical Report Vol. 45, No. 1 (2005-3) (hereinafter referred to
as Non-Patent Document 1). Water heated by the heat exchanger
downstream of the air heater is utilized as a heat source for the
heat exchanger provided downstream of the desulfurization system.
Hereinafter, the former heat exchanger is referred to as a heat
recovery heat exchanger and the latter heat exchanger is referred
to as a re-heating heat exchanger. The re-heating heat exchanger is
provided for preventing steams discharged out of a chimney from
forming white smoke that results in visual pollution. In a place
where such regulation is imposed, installation of the re-heating
heat exchanger is legally obliged.
[0005] Further, CO.sub.2 in the exhaust gas can be separated and
captured by providing a CO.sub.2 capture system downstream of a
desulfurization system. As a method of separating and capturing
CO.sub.2 in the exhaust gas, a method of absorbing CO.sub.2 in a
CO.sub.2 adsorbing column by using an amine solution including MEA
(monoethanol amine), etc. which is applied to separation and
capture of CO.sub.2 in the exhaust gas from a boiler or a gas
turbine. For improving a CO.sub.2 capturing efficiency, various
amine compounds have been proposed (for example, refer to Japanese
Patent Publications Nos. 3761960 and 3771708). The amine compound
has a high ability of separating and capturing CO.sub.2. However,
since the amine compound is poisoned by oxygen or SO.sub.x, etc. in
the exhaust gas or scatters partially from the CO.sub.2 absorption
column, supplementation of the amine compound is necessary to
increase the cost.
[0006] Then, a CO.sub.2 capture system using a CO.sub.2 solid
sorbent which is less poisoned by oxygen, SO.sub.x, etc. in the
exhaust gas and less scatters has been studied. For example, a
system of having four columns packed with a CO.sub.2 solid sorbent
and capturing CO.sub.2 by four steps of (1) sorbing CO.sub.2 by a
sorbent, (2) purging the inside of the column, (3) desorbing
CO.sub.2 from the sorbent, and (4) cooling the sorbent is disclosed
in NEDO Report, Hei 14 (2002), Development for Effective
Utilization of Technique of Fixing Carbon Dioxide for Practical
Use, and Development for CO.sub.2 Separating and Capturing
Technique by Chemical Adsorption, by Shikoku Research Institute
(2003-3) (hereinafter referred to as Non-Patent Document 2).
[0007] Further, a technique capable of downsizing the system by
constructing a rotational driving type CO.sub.2 capture system
using a CO.sub.2 solid sorbent is described in "CO.sub.2
Separation/capture and Store/Isolation Technique", published from
NTS (2009) 76 (hereinafter referred to as Non-Patent Document
3).
[0008] On the other hand, for the hear efficiency of a boiler, a
heat efficiency of an electric power generation system is improved
generally by re-heating a condensate generated from a condenser
provided downstream of a steam turbine by steams extracted from the
steam turbine.
[0009] In a case where the re-heating exchanger is not present,
heat recovered by the heat recovery heat exchanger can be utilized
in other uses. For example, Japanese Unexamined Patent Application
Publication No. S60 (1985)-227845 describes a method of heating a
condensate by using heat recovered from a boiler exhaust gas by a
heat recovery heat exchanger thereby improving the heat efficiency
of the boiler (refer to FIG. 5).
[0010] Further, Japanese Patent Unexamined Application Publications
Nos. H03 (1991)-193116 and 2010-240617 describe that the heat
efficiency of a boiler is improved by heating a condensate
utilizing the heat of captured CO.sub.2 which is generated from a
CO.sub.2 capture system using an amine solution.
SUMMARY
[0011] When CO.sub.2 is recovered by using a CO.sub.2 solid
sorbent, heat is generated upon sorption (absorption heat and
adsorption heat) and, further, air, etc. possessing some heat are
generated upon cooling of the sorbent. In the CO.sub.2 capture
system shown in the Non-Patent Documents 2, 3, such heat energy
cannot be re-utilized sufficiently, which may lower the heat
efficiency of the boiler due to the energy used for capturing
CO.sub.2. Japanese Patent Publications Nos. 3761960 and 3771708 do
not describe a method for coping with the lowering of the heat
efficiency of the boiler. The method shown in Japanese Unexamined
Patent Application Publication No. S60 (1985)-227845 does not
describe the effective utilization of heat generated from the
CO.sub.2 capture system and improvement in the heat efficiency is
insufficient. Further, since the re-heating heat exchanger is not
used, this results in a disadvantage of generating white smoke from
a chimney. Japanese Unexamined Patent Application Publication Nos.
H03 (1991)-193116 and 2010-240617 only show the technique of
utilizing heat of the CO.sub.2 gas emitted from the amine solution
and do not show an optimal heat recovery method in a case of using
the CO.sub.2 solid sorbent and improvement in the heat efficiency
of the boiler is insufficient.
[0012] The present invention intends to improve the heat efficiency
of a boiler that separates and captures CO.sub.2 from an exhaust
gas using a CO.sub.2 solid sorbent and, specifically, it intends to
provide a heat recovery system and a heat recovery method capable
of efficiently recovering the heat energy generated from a system
for capturing CO.sub.2, and a CO.sub.2 sorbent used therefor.
[0013] A heat recovery system of a boiler according to the
invention has a CO.sub.2 capture system of capturing CO.sub.2
contained in an exhaust gas by using a CO.sub.2 solid sorbent and
increases the temperature of a fluid concerned with the boiler by
using a gas generated from the CO.sub.2 capture system.
[0014] According to the invention, the heat efficiency of the
boiler can be improved remarkably by efficiently recovering the
heat generated from the CO.sub.2 capture system. Further, it can
prevent generation of white smokes from a chimney while suppressing
lowering of the heat efficiency.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a view showing an embodiment of an existent boiler
exhaust gas purifying system;
[0016] FIG. 2 is a view showing a system for improving the heat
efficiency of a boiler by an existent method;
[0017] FIG. 3 is a view showing a CO.sub.2 capture system using a
CO.sub.2 sorbent;
[0018] FIG. 4 is a view showing a system for increasing the
temperature of a condensate by using an exhaust gas from a CO.sub.2
capture system;
[0019] FIG. 5 is a view showing a system for increasing the
temperature of a gas flowing into a boiler by using an exhaust gas
from the CO.sub.2 capture system; and
[0020] FIG. 6 is a view showing a system for increasing the
temperature of a gas flowing into a chimney by using an exhaust gas
from the CO.sub.2 capture system.
DETAILED DESCRIPTION
[0021] The present invention is to be described specifically.
[0022] Generally, for improving the heat efficiency of a boiler, a
steam turbine that generates electric power by steams which
received heat at a boiler and a condenser for condensing the steams
at the downstream thereof are provided, and a condensate obtained
by condensation is heated by steams extracted from the steam
turbine, thereby improving the heat efficiency of the electric
power generation system. Further, in Japanese Unexamined Patent
Application Publication No. S60 (1985)-227845, the heat efficiency
of the power generation system is further improved by heating water
condensed by the condenser using the heat of a boiler exhaust gas
by passing through a heat exchanger. However, since the heat of the
boiler exhaust gas is used for increasing the temperature of the
condensate, the temperature of the exhaust gas at the upstream of a
chimney cannot be increased, which may possibly lead to generation
of the white smoke.
[0023] The present inventors have made an earnest study and, as a
result, have found that white smoke generated from a chimney can be
suppressed while also improving the heat efficiency of an electric
power generation system in a boiler system comprising a power
generation system having a boiler, a steam turbine that generates
electric power by steams which received heat at a boiler, a
condenser provided at the downstream thereof for condensing the
steams, a heater for heating the condensed water with steams
extracted from the steam turbine and, further, a CO.sub.2 capture
system for sorbing and capturing a CO.sub.2 gas in an exhaust gas
exhausted from the boiler by a solid CO.sub.2 sorbent, and a
chimney for discharging the exhaust gas after capturing CO.sub.2 by
the CO.sub.2 capture system, or an exhaust gas exhausted from the
boiler, in which the temperature of a fluid concerned with the
boiler system is increased by using the exhaust gas exhausted from
the CO.sub.2 capture system.
[0024] The boiler as a target of the invention is not particularly
restricted so long as a heat recovering steam turbine is provided.
The invention is applicable to a system including a gas-fired
boiler, a coal-fired boiler, or a gas turbine as the boiler, as
well as to IGCC (integrated coal gasification combined cycle).
[0025] As the fluid concerned with the boiler system, water
condensed by the condenser, a gas flowing into the boiler, and an
exhaust gas exhausted from the boiler may be considered.
(Increase of Temperature of Condensate)
[0026] The heat efficiency of the electric power generation system
can be improved by partially or entirely heat-exchanging water
condensed by the condenser with the exhaust gas exhausted from the
CO.sub.2 capture system by using a heat exchanger and increasing
the temperature thereof. In the invention, a solid CO.sub.2 sorbent
is used as the CO.sub.2 capture system. In this case, the
temperature of the exhaust gas exhausted from the CO.sub.2 capture
system may sometimes reach 100.degree. C. to 500.degree. C.
depending on the type of the CO.sub.2 sorbent. Japanese Unexamined
Patent Application Publication No. H03 (1991)-193116 describes that
the turbine output is improved by 0.3% to 0.4% based on a trial
calculation in a case of a CO.sub.2 exhaust temperature at
85.degree. C. When a solid CO.sub.2 sorbent is used, a further
improvement can be expected in the turbine output.
[0027] Further, in this case, white smoke can be prevented, for
example, by recovering the heat of the boiler exhaust gas at the
downstream of the air heater by the heat recovery heat exchanger
and increasing the temperature of the exhaust gas at the upstream
of the chimney by using the re-heating heat exchanger.
(Increase of Temperature of Gas Flowing into Boiler)
[0028] The heat efficiency of the boiler is improved by increasing
the temperature of a gas flowing into the boiler by using the
exhaust gas exhausted from the CO.sub.2 capture system. In the
existent technique, air at about room temperature is heated to
about 300.degree. C. by using an air heater and then caused to flow
into the boiler. However, when the temperature of air is increased
to about 100.degree. C. by using the exhaust gas exhausted from the
CO.sub.2 capture system, the temperature of the air flowing into
the boiler after passing through the air heater can also be
increased to about 350.degree. C. In this case, since the
temperature of the boiler exhaust gas is increased by about
50.degree. C., when a heat recovery heat exchanger is provided to
the downstream of the air heater and the temperature of water
condensed by the condenser can be increased partially or entirely
more effectively by using the heat exchanger, and the heat
efficiency of the electric power generation system is improved. In
this case, the electric power generation efficiency of the boiler
is improved by about 2.1%.
[0029] Further, in this case, white smoke can be prevented
effectively by partially or entirely using the heat recovered by
the heat recovery heat exchanger for increasing the temperature of
the exhaust gas at the upstream of the chimney by using a
re-heating heat exchanger.
[0030] Means for increasing the temperature of the gas flowing into
the boiler by using the exhaust gas exhausted from the CO.sub.2
capture system is not particularly restricted. For example, the
exhaust gas exhausted from the CO.sub.2 capture system and a gas
including air can be heat-exchanged by using a heat exchanger.
Species of a gas generated from the CO.sub.2 capture system
include, for example, N.sub.2, O.sub.2, CO.sub.2, H.sub.2O, air,
etc. In this case, there is a merit that the gas can be used
irrespective of the species.
[0031] Alternatively, the exhaust gas exhausted from the CO.sub.2
capture system can be used partially or entirely as a gas flowing
into the boiler. The exhaust gas generated from the CO.sub.2
capture system may sometimes contain CO.sub.2, which may lower the
CO.sub.2 recovery efficiency if the gas is released to atmospheric
air. By letting the exhaust gas generated from the CO.sub.2 capture
system partially or entirely flow into the boiler, CO.sub.2 is
again taken into the boiler and flows through the exhaust gas
purification system into the CO.sub.2 capture system to improve the
CO.sub.2 capturing efficiency.
(Increase of Temperature of Boiler Exhaust Gas)
[0032] Generation of white smoke from the chimney can be suppressed
by increasing the temperature of a gas flowing into the chimney by
using the exhaust gas exhausted from the CO.sub.2 capture system.
Specifically, the temperature of the gas flowing into the chimney
can be increased when the gas flowing into the chimney partially or
entirely comprises the exhaust gas exhausted from the CO.sub.2
capture system.
[0033] Alternatively, the temperature of the gas flowing into the
chimney can be increased by providing a heat exchanger for
increasing the temperature of a gas flowing into the chimney and
performing heat exchange with the exhaust gas exhausted from the
CO.sub.2 capture system. When the exhaust gas generated from the
CO.sub.2 capture system contains CO.sub.2 and flows as it is into
the chimney, once captured CO.sub.2 is emitted into atmospheric
air. In a case of using the heat exchanger, since the CO.sub.2 gas
after heat exchange can be captured by flowing CO.sub.2 after heat
exchange into a compressor, such disadvantage can be overcome.
(CO.sub.2 Capture System)
[0034] The CO.sub.2 capture system is not particularly restricted
providing that the system utilizes the CO.sub.2 sorbing effect of
the solid CO.sub.2 sorbent. As the CO.sub.2 capture system, it may
be considered to provide four CO.sub.2 sorbing columns packed with
a CO.sub.2 sorbent. In this case, as the CO.sub.2 capturing
process, (a) CO.sub.2 sorbing step, (b) purging step for the inside
of the CO.sub.2 sorption column, (c) desorbing step of CO.sub.2 and
(d) cooling step for the inside of the CO.sub.2 sorption column may
be considered and CO.sub.2 in the exhaust gas can be captured at a
high level by corresponding the following four steps (a) to (d)
successively to each of the four CO.sub.2 sorption columns.
(a) CO.sub.2 sorption: CO.sub.2 gas in the exhaust gas is sorbed by
letting an exhaust gas flow into the CO.sub.2 sorption column. (b)
Purging for the inside of CO.sub.2 sorption column: After sorbing
CO.sub.2, inside of the CO.sub.2 sorption column is purged by
flowing a gas into the CO.sub.2 sorption column. As a purge gas, a
CO.sub.2 gas at a high purity is used preferably for increasing the
concentration of captured CO.sub.2. (c) CO.sub.2 desorption: Then,
a gas is caused to flow for desorbing CO.sub.2 from the sorbent and
the desorbed CO.sub.2 gas is captured. For desorbing CO.sub.2 from
the sorbent, it is necessary to heat the sorbent. The quantity of
heat to be applied is different depending on the sorbent. It is
necessary to increase the temperature of the sorbent to a
temperature at which CO.sub.2 is desorbed from the sorbent. As a
method of applying the heat, it may be considered, for example, to
extract steams generated in the steam turbine and cause the steams
to flow through the CO.sub.2 sorption column. Further, a method of
obtaining heat from other CO.sub.2 sorption column by way of a heat
exchanger may also be considered. (d) Cooling for the inside of the
CO.sub.2 sorption column: Further, it is necessary to lower the
temperature of the sorption column once increased in the CO.sub.2
desorption step described above to a temperature suitable to the
CO.sub.2 sorbing step. As a method of lowering the temperature, it
may be considered to flow a gas at a temperature lower than that of
the sorption column. Use of atmospheric air at room temperature may
be considered as an example. Further, (b) when the CO.sub.2 gas is
used for purging in the purging step for the inside of the CO.sub.2
sorption column, CO.sub.2 may sometimes flow out of the CO.sub.2
sorption column. In this case, the gas flowing out of the CO.sub.2
sorption column can also be used as a gas for lowering the
temperature of the CO.sub.2 sorption column by letting the gas flow
into the CO.sub.2 sorption column during the cooling step (d) in
the CO.sub.2 sorption column. By using the method, CO.sub.2 once
flowing out in the purging step can be caused to flow again into
the sorption column to improve the CO.sub.2 recovery efficiency.
Japanese Unexamined Patent Application Publication Nos. H03
(1991)-193116 and 2010-240617 disclose a technique of recovering
the heat of the CO.sub.2 gas desorbed from the amine solution, but
any gas generated from the CO.sub.2 sorption column at the steps
(a) to (d) can be used when the solid CO.sub.2 sorbent is used.
[0035] The gas flowing out of the CO.sub.2 sorption column may
include, for example, N.sub.2, O.sub.2, CO.sub.2, steams, air, etc.
Since the flowing out gas has a sorption heat in the sorption
column (adsorption heat, absorption heat, heat transferred from the
sorbent), etc. the gas reaches a temperature at about 50.degree. C.
to 500.degree. C. By recovering the heat of the flowing out gas by
the technique shown in the present specification, the heat
efficiency of the electric power generation system can be
improved.
[0036] The CO.sub.2 sorbing material is not particularly restricted
so long as the sorbent comprises a material capable of sorbing
CO.sub.2 and preferred ingredient includes, for example, Ce, Pr,
Nd, Sm, Gd, etc. The CO.sub.2 recovery efficiency is improved
particularly by the use of Ce. The chemical form of the ingredient
is not particularly restricted. The chemical form of the ingredient
may include, for example, metal, oxide, organic compound, and
chloride, and the oxide form is particularly preferred. The oxide
suffers from less degradation due to the use and can be used for a
long time.
[0037] The structural form of the CO.sub.2 sorbent includes, for
example, that of granule, lump, sphere, pellet, honeycomb, mesh,
etc. and the structural form can be selected in accordance with the
operation state of the CO.sub.2 capture system, to which the
sorbent is applied.
[0038] The CO.sub.2 sorbent preferably has a specific surface area
of 3 m.sup.2/g or more. When the specific surface area is small,
the CO.sub.2 capturing performance is decreased and the provision
of the system gives less effect.
[0039] The ingredient may be supported, for example, on a porous
support such as alumina or zeolite. The ingredient can be dispersed
highly and the CO.sub.2 sorbing performance can be improved further
by supporting the ingredient on the porous support having a
specific surface area of 10 m.sup.2/g or more.
[0040] As the preparation method of the CO.sub.2 sorbent, physical
preparation method, for example, an impregnation method, a kneading
method, a coprecipitation method, a sol-gel method, an ion exchange
method, a vapor deposition method, a spray dry method, etc., and
preparation methods utilizing the chemical reaction can be
used.
[0041] As the starting material for the CO.sub.2 sorbent, various
compounds, for example, nitrate compounds, chlorides, acetate
compounds, complex compounds, hydroxides, carbonate compounds, and
organic compounds, as well as metals, or metal oxides can be
used.
[0042] Preferred embodiments of the invention are to be described
with reference to the drawings.
(Example of Existent Exhaust Gas Purifying System)
[0043] FIG. 1 shows an example of an exhaust gas processing system
for a coal-fired boiler having a CO.sub.2 capture system using a
CO.sub.2 solid sorbent. Coal and air are supplied to a coal-fired
boiler 1, and the coal is burnt. The temperature of a combustion
exhaust gas reaches 1600 to 1800.degree. C. The temperature of the
exhaust gas is lowered by a not-illustrated heat exchanger in the
boiler and then introduced into an NO reduction system 2. In the NO
reduction system, ammonia (hereinafter referred to as NH.sub.3) is
supplied to reduce and detoxify NO into nitrogen (hereinafter
referred to as N.sub.2) by using a NO.sub.x reduction catalyst.
Further, the exhaust gas is introduced into an air heater 3 and
heat-exchanged with air 11 (boiler combustion gas). Air 11 is
supplied from atmosphere air by a gas supply blower 10 (hereinafter
referred to as FDF), heated by the air heater 3 and used as a
combustion air in the coal-fired boiler 1. The exhaust gas
introduced into a heat recovery heat exchanger (hereinafter
referred to as a heat recovery GGH4) is heat-exchanged with water
in the heat recovery GGH4, then removed with dusts and soots by a
dust removal system 5, and removed with SO.sub.x in a
desulfurization device 6. On the other hand, the temperature of the
exhaust gas is increased by the reheating exchanger (hereinafter
referred to as a reheating GGH8) by using water warmed by the heat
recovery GGH4, and the exhaust gas is released from a chimney 9 at
such a temperature that steams do not form white smoke. The
re-heating heat exchanger is provided for preventing visual
pollution caused by white smoke. If white smoke comprises steams,
there is no environmental problem and installation thereof may not
be legally obliged depending on the location.
Comparative Embodiment
[0044] As a method of improving the heat efficiency by proceeding
heat recovery in the exhaust gas processing of a coal-fired boiler,
a technique as shown in FIG. 2 is considered. This technique
concerns an exhaust gas processing system not providing a
re-heating heat exchanger and this is a system of improving the
heat efficiency of the boiler by utilizing heat recovered by a heat
recovery GGH4.
[0045] A steam turbine 23 is driven by heat-recovered steams of a
coal-fired boiler 1, and steams at the exit are cooled and
condensed by a condenser 24. The formed condensate is sent to a
heater 26 and heated by steams 25 extracted from the steam turbine
23. The heated condensate is sent to the boiler 1 to drive the
steam turbine 23 again as a circulating cycle.
[0046] As shown in FIG. 2, a system of partially or entirely
passing a condensate generated from the condenser 24 through the
heat recovery GGH4 to increase the temperature of the condensate
thereby improving the efficiency of the heat recovery has been
considered as the existent technique. However, although this method
improves the heat efficiency, a disadvantage not capable of
preventing generation of white smoke from the chimney occurs since
the re-heating exchanger is not present. Further, heat generated
from the CO.sub.2 capture system cannot be utilized.
First Embodiment
Example of CO.sub.2 Capture System
[0047] As a CO.sub.2 capture system that can be used in the
technique of the invention, a system shown in FIG. 3 may be
considered.
[0048] CO.sub.2 sorbent packed columns 20 as containers for
incorporating a CO.sub.2 sorbent shown by four units in FIG. 3 each
have an identical function. Each of the four units of the CO.sub.2
sorbent packed columns 20 incorporating the CO.sub.2 sorbent
continuously repeats four steps, that is, a CO.sub.2 sorbing step,
a CO.sub.2 purging step, a CO.sub.2 desorbing step, and a column
cooling step successively.
[0049] At the first step (CO.sub.2 sorbing step), a
CO.sub.2-containing gas which is an exhaust gas flowing from a
channel 18 for CO.sub.2-containing gas is caused to flow only to
one of the four units of the CO.sub.2 sorbent packed columns 20
incorporating the CO.sub.2 sorbent, and CO.sub.2 is sorbed by the
CO.sub.2 sorbent. The gas after removing CO.sub.2 is exhausted from
a gas exhaust port 21 or a pipeline 22 connected with a CO.sub.2
compressor to the outside of the column. After it is judged that
CO.sub.2 sorption by the CO.sub.2 sorbent reaches saturation, flow
of the CO.sub.2-containing gas from the channel 18 for
CO.sub.2-containing gas to the CO.sub.2 sorbent packed column 20
incorporating the CO.sub.2 sorbent is stopped.
[0050] At the second step (CO.sub.2 purging step), CO.sub.2 is
caused to flow from a channel 15 for high purity CO.sub.2 gas into
the CO.sub.2 sorbent packed column 20 to purge gases other than
CO.sub.2. The gases discharged in this step are exhausted from the
gas exhaust port 21 or the pipeline 12 connected with the CO.sub.2
compressor to the outside of the column. Finally, flow of the
CO.sub.2-containing gas is stopped.
[0051] At the third step (CO.sub.2 desorbing step), the temperature
of the CO.sub.2 sorbent packed column 20 is increased and steams
are caused to flow from a steam gas channel 16, by which CO.sub.2
sorbed in the CO.sub.2 sorbent is desorbed and exhausted from the
gas exhaust port 21 or the pipeline 22 connected with the CO.sub.2
compressor to the outside of the column.
[0052] At the fourth step (column cooling step), air at room
temperature is caused to flow from an air channel 17 to the
CO.sub.2 sorbent packed column 20, by which the CO.sub.2 sorbent
and the CO.sub.2 sorbent packed column 20 incorporating the
CO.sub.2 sorbent are cooled.
[0053] By repeating the four steps described above in each of the
four units of containers incorporating the CO.sub.2 sorbent, the
operation of the system of capturing CO.sub.2 continuously from the
CO.sub.2-containing gas can be attained.
[0054] It is considered that the gas exhausted at each of the steps
is at a temperature of about 40.degree. C. to 500.degree. C.,
depending on the species and the temperature of the gas flowing
into the CO.sub.2 sorbent packed column 20 incorporating the
CO.sub.2 sorbent and, further, the type of the CO.sub.2
sorbent.
(Example of System to Increase the Temperature of Condensate)
[0055] FIG. 4 is a view showing an example of a system for
increasing the temperature of a condensate through heat exchange
between a condensate obtained by condensation in a condenser 24,
and a gas exhausted from a CO.sub.2 sorbent packed column 20 which
as the container for incorporating a CO.sub.2 sorbent. As a gas
flowing into a heat recovery GGH4, a gas discharged from the
CO.sub.2 sorbent packed column 20 for incorporating the CO.sub.2
sorbent at any of the CO.sub.2 capturing step, the CO.sub.2 purging
step, CO.sub.2 desorbing step, and the column cooling step may be
used. However, a CO.sub.2 gas exhausted from the CO.sub.2 sorbent
packed column 20 for incorporating the CO.sub.2 sorbent in the
CO.sub.2 desorbing step is passed through the heat recovery GGH4,
compressed by a compressor, and then recovered. The condensate
whose temperature is increased by the heat recovery GGH4 is passed
through a heater 26 and then sent to the boiler 1 thereby
contributing to the improvement of the power of the electric power
generation system. Improvement of 0.4% or more can be expected for
the turbine output depending on the capacity of the boiler.
[0056] In addition, when the system shown in FIG. 1 is combined,
and the heat recovery GGH4 and the re-heating GGH8 are used
together, generation of white smoke from the chimney can also be
suppressed.
[0057] With the result described above, as shown in this
embodiment, the boiler output can be improved and the generation of
the white smoke from the chimney can be suppressed simultaneously
in the system of increasing the temperature of a fluid concerned
with the boiler system by using the exhaust gas exhausted from the
CO.sub.2 capture system, by adapting the system, for example, as
the heat recovery GGH4 that performs heat exchange between the
condensate and the gas exhausted from the CO.sub.2 sorbent packed
column 20.
Second Embodiment
[0058] FIG. 5 is a view showing an example of a system using a gas
exhausted from a CO.sub.2 sorbent packed column 20 as a container
for incorporating a CO.sub.2 sorbent as a combustion gas of a
boiler 1. The system also has a device of performing heat exchange
between a condensate condensed by a condenser 24 and a boiler
exhaust gas through a heat recovery GGH4.
[0059] As the gas flowing into a gas supply blower 10, a gas
exhausted from a CO.sub.2 sorbent packed column 20 incorporating a
CO.sub.2 sorbent in the process of a CO.sub.2 sorbing step, a
CO.sub.2 purging step, or a column cooling step can be used. When
the temperature of a gas flowing into an air heater 3 is heated
from 30.degree. C. to 100.degree. C. by using the gas exhausted
from the CO.sub.2 sorbent packed column 20, the temperature of the
exhaust gas flowing into the heat recovery GGH4 is increased by
about 50.degree. C. Accordingly, the temperature of the condensate
undergoing heat exchange by the heat recovery GGH4 can be increased
effectively to improve the boiler output. In this case, the
electric power generation efficiency of the boiler system is
improved by about 2.1%.
[0060] Further, when the gas exhausted from the CO.sub.2 sorbent
packed column 20 as a container in the CO.sub.2 purging step is
used as the gas flowing into the gas supply blower 10, a small
amount of CO.sub.2 may sometimes be contained in addition to
N.sub.2 and O.sub.2 as the species of the gas exhausted from the
CO.sub.2 sorbent packed column 20. In this case, since the CO.sub.2
gas can be caused to flow again into the boiler in this system, the
CO.sub.2 gas can be sorbed again by the CO.sub.2 capture system by
way of the exhaust gas purification system. Accordingly, CO.sub.2
capturing efficiency is improved.
[0061] In this embodiment, the system is adapted to use the gas
exhausted from the CO.sub.2 sorbent packed column 20 as the
combustion gas for the boiler 1. It is also possible to use
atmospheric air as a combustion gas for the boiler 1 after
increasing the temperature of the atmospheric air by heat exchange
with the gas exhausted from the CO.sub.2 sorbent packed column 20.
In this case, a gas exhausted from the CO.sub.2 sorbent packed
column 20 incorporating a CO.sub.2 sorbent at any of the CO.sub.2
sorbing step, the CO.sub.2 purging step, the CO.sub.2 desorbing
step, and the column cooling step can be used as the gas flowing
into the gas supply blower 10.
[0062] With the result described above, as shown in this
embodiment, the boiler output can be improved in the system of
increasing the temperature of the fluid concerned with the boiler
system by using the exhaust gas exhausted from the CO.sub.2 capture
system, in which the temperature of the gas flowing into the boiler
is increased using the exhaust gas exhausted from the CO.sub.2
capture system, by adapting the system such that the exhaust gas
exhausted from the CO.sub.2 sorbent packed column 20 partially or
entirely comprises the combustion gas flowing to the boiler 1 or by
adapting the system, for example, as a heat recovery GGH that
performs heat exchange between air and the gas exhausted from the
CO.sub.2 sorbent packed column 20 to increase the temperature of
the air and use the air as the combustion gas of the boiler 1.
Third Embodiment
[0063] FIG. 6 is a view showing an embodiment of a system of
letting a gas exhausted from a CO.sub.2 sorbent packed column 20 as
a container for incorporating a CO.sub.2 sorbent flow into a gas at
the upstream of a chimney 9. As the gas flowing into the gas
upstream of the chimney 9, a gas exhausted from the CO.sub.2
sorbent packed column 20 for incorporating the CO.sub.2 sorbent at
the CO.sub.2 sorbing step, the CO.sub.2 purging process, or the
column cooling step can be used. Generally, the temperature of a
gas exhausted from a desulfurization device 6 is at about 40 to
50.degree. C. and, when the temperature of the gas is increased to
about 90.degree. C. by flowing the gas exhausted from the CO.sub.2
sorbent packed column 20 for incorporating the CO.sub.2 sorbent to
the gas at the upstream of the chimney 9, generation of the white
smoke from the chimney 9 can be prevented. Further, the boiler
output can be improved also by using the system as shown in FIG. 2
together and performing heat exchange between the condensate
condensed by the condenser 24 and the boiler exhaust gas in the
heat recovery GGH4.
[0064] In this embodiment, the system is adapted such that the gas
exhausted from the CO.sub.2 sorbent packed column 20 as a gas
flowing into the gas at the upstream of the chimney 9, the
temperature of the gas flowing into the chimney 9. Alternatively,
the temperature of the gas flowing into the chimney 9 can be
increased also by performing heat exchange between the gas
exhausted from the desulfurization device 6 and the gas exhausted
from the CO.sub.2 sorbent packed column 20. As the gas exhausted
from the CO.sub.2 sorbent packed column 20, a gas exhausted from
the CO.sub.2 sorbent packed column 20 incorporating the CO.sub.2
sorbent at any of the CO.sub.2 sorbing step, the CO.sub.2 purging
step, the CO.sub.2 desorbing step, or the column cooling step can
be used.
[0065] With the result described above, as shown in this
embodiment, the boiler output can be improved and generation of the
white smoke from the chimney can be prevented in a system of
increasing the temperature of the fluid concerned with a boiler
system using the exhaust gas exhausted from the CO.sub.2 capture
system by adapting the system such that the gas flowing into the
chimney 9 contains the gas exhausted from the CO.sub.2 sorbent
packed column 20, or adapting the system, for example, as a heat
recovery GGH of increasing the temperature of a gas flowing into
the chimney 9 by heat exchange between the gas exhausted from the
desulfurization device 6 and the gas exhausted from the CO.sub.2
sorbent packed column 20.
[0066] The present invention is not restricted to the embodiments
described above but includes various modified embodiments. For
example, the embodiments described above have been described
specifically for easy explanation of the present invention but are
not always restricted to those having all constituent factors
described therein. Further, a portion of the constitution of one
embodiment can be replaced with the constitution of other
embodiments, or a constitution of one embodiment can be added to
that of other embodiments. Further, for a portion of a constitution
in each of the embodiments, addition, deletion or replacement of
other constitution are possible.
* * * * *